Sunday, July 31, 2011

Of electricity wires and the sad plight of comic book idols

by Uditha Wijesena

Bats in their mythological role are famous as symbols of darkness and ghostlike mystery. In Europe and many other cultures demons are pictured with the wings of bats while fairies and angels are adorned with wings of feathers.

The electricution of the flying foxes

Bats are victims of many more superstitions in the west, but in Chinese and other far-eastern cultures they are a symbol of fortune, happiness and longevity. And of late the 'Batman' a comic book idol.

Bats have been useful to man in some parts of the world as a food source. The large flying fox weighing over a kilogram is being consumed by the natives of Africa and Australia even today. This is also the case in some Asian countries.

The accumulations of their droppings at their roosts have been collected and used as fertilizer in agriculture and also during war times as a source of nitrate for gunpowder. They help in pest control in agriculture during the night but the larger fruit bats themselves are pests in the orchards.

Sri Lanka has a total of 15 Genera and 30 Species of bats. [Weerakoon et al-The Fauna of Sri Lanka 2006 IUCN] of them the largest and the most prominent is the Giant Fruit Bat, Peropus giganteus, more commonly known as the Flying Fox. The Sinhalese name is Ma-wawula and in Tamil Periya-vaval.

There isn't much knowledge of the bats in Sri Lanka to the ordinary layman other than to a biologist who may have studied bats, but for the day to day encounter of the flying fox that roosts in the open close to human habitation.

This bat is active mostly in the evening and night. It has large well developed eyes for guidance in the night and only sees in black and white. It does not use high frequency orientation sounds for echolocation in the dark. It finds its food by smell and will fly to distances of up to as much as 20 miles to feeding areas. The face looks that of a fox, thus the name flying fox. It has grayish brown or black fur on its body with the shoulders often in golden yellow fur.

It roosts primarily in trees in very large colonies of up to 800 or 1000 individuals both male and female. However the males have a ranking order while roosting; the dominant males at the top of the tree and the subsequent lower ranking males in the lower levels of the tree.

The hierarchy of the males is governed by its size and the strength. The males retain their roosting position in the tree while the females move around from day to day. All the more the males are very possessive of females during the mating season.

The females have a gestation period of 140 to 150 days and give birth to a single pup that is carried by the mother in flight for up to six to seven weeks to fly by its self in eleven [11] weeks. The pup is not weaned until five months.

The flying fox lives mainly on the pulp and juices of the flowers and fruits of many species of trees in their seasons. Therefore it is considered an agricultural pest. The seasonal rambutan fruit finds a death trap to many flying foxes in the Malwana area.

Farmers in these areas were in the habit of illuminating the trees to ward away the intruding bats, but with the high cost of electricity some are in the habit of electrocuting the bats.

It is disheartening to hear of such inhuman acts for economic benefit while bats have been a very vital source in the maintenance and expansion of forests, by seed dispersion and pollination. At times it is funny to see intoxicated flying foxes not being able to take wing from the toddy collecting pots on coconut palms during the toddy tapping season in the coast.

Other than the killing of flying foxes for food and seasonal destruction of them on cash crop trees, the electrical power transmission also takes a fair number of mortality annually in the urban areas. One example could be the city of Kandy with one of the largest roosting camps in the Peradeniya gardens.

The low voltage electricity transmission lines are specified to have a ground clearance to the lowest transmission line of 5.2 metres. [17 feet] The spacing of the transmission line on the poles is at 300 millimetre intervals. [1 foot] The morphology of an adult flying fox has a body measurement of nine to twelve inches with a wing span of five and a half feet.

These dimensions are an ideal situation for electrocution of flying foxes on low frequency transmission lines in the cities. If one is to observe these rotting carcasses proper they seem to be closer to the poles or to the spacer rods on the lines controlling the sag. Where the sag is larger the bats escape death.

In developed countries naked wires are no longer used for transmission. The insulated bundle cables are now used for safety and efficiency. It is high time we change to these cables in updating our electricity services in the cities as being done in some cities in Sri Lanka.

We derive safety standards for humans and in doing so we have no right to ignore the habits and uses of other living beings but to accommodate them in these standards as well, for the simple reason that the fruit bat gives birth to only one pup in an year and it has a life span of fifteen years. This however is now definitely shorter with the fast denuding forest cover, and the dwindling of the available feeding areas of the flying fox.

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BAT, is the common name for flying mammals belonging to the order Chiropetra in biological science. It is derived from the Greek meaning 'hand wing'. Bats, birds and insects are the only animals that can sustain themselves in the air, and of them it is only the bats that are entirely a flying group.

There are no bats that cannot fly and they are perhaps the only animals that commonly live in the deepest and in the totally dark parts of caves where they hang upside down.

Their hind feet are adapted to hang from twigs or rough surface of a rock and they hang upside down securely while in deep sleep, in hibernation or even after death. Bats have a shorter geological history when compared to birds.

The oldest fossil bird date to about 130-160 million years whereas the oldest fossil bat is about 60 million years by date. This short geological history of bats accounts in some measure to their anatomy being closer to their non-flying ancestors on ground. For example the bird bones are penetrated by air spaces while those of bats are of the same basic structure of other mammals.

It has been shown that bats from their evolutionary beginnings have been auditory animals which listened in the darkness even when they were of the tree climbing forms that jumped and glided before their descendants took to the air. The birds on the other hand may have evolved from ancestors that used their eyes more than their ears.

Scientists have now derived that most bat species find their way in darkness by emitting high frequency orientation sounds and receiving the echoes as they bounce off objects.

Bats differ from other mammals as their body temperature and metabolism fluctuate rapidly and with much ease; when fully awake and active a bat has a body temperature between 1000 and 1050 F. This is the case in cold winter air or in hot warm summer and in the tropics.

The large surface area of the wings facilitate heat loss by the blood vessels dilating to take in more blood in warm conditions and the blood vessels constricting in cooler climes restricting the volume of blood flow.

When at rest their body temperature may drop to 800 or 900 F in summer and to 350 or 400 F in the winter. The activity of an animal is roughly proportional to its body temperature; a bat cannot fly until its body temperature reaches 800 F. This is why bats are often found to be lethargic and fail to respond or fly off for some time after they are first disturbed.